Why Are Women More Likely to Develop Thyroid Disorders?

Women are more prone to autoimmunity, in which the immune system mistakenly attacks the body's own cells. More than 100 types of autoimmune disorders have been identified, and 80 percent of people diagnosed are women. Autoimmune disorders, including Grave's disease and Hashimoto's disease, are the most common causes of thyroid dysfunction.

As for why, researchers aren't sure. In fact, scientists have yet to determine what causes autoimmunity. However, according to the National Institute of Allergy and Infectious Diseases, a mixture of environmental and genetic factors likely contributes.

Environmental factors

Research suggests genetics are about 30 percent responsible for autoimmunity, while the other 70 percent is attributable to environmental factors, including toxic chemicals, dietary components, occupation, infections and gut dysbiosis.

Stress is thought to contribute, too.

"Another contributing factor that needs to be explored, but is largely ignored in the medical research, is that to a significant degree, our immune system is directed by whether we feel safe," said Jacob Teitelbaum, M.D., an internist in Kailua-Kona, Hawaii, in an email interview. "If you feel unsafe, your immune system may be on widespread overdrive, followed by exhaustion and difficulty distinguishing friend from foe. So the societal rise in fear and divisiveness may be a potent contributor, especially for women who often are concerned not only about sexual safety but have occupations in male-dominated workplaces."

Genetics

Autoimmune disorders and thyroid conditions tend to run in families, signaling a genetic component. The X chromosome—of which women have two and men have one—carries more genes linked to autoimmune diseases. This could be another reason women are more likely to develop such conditions, according to Rashmi Roy, M.D., a thyroid surgeon at Clayman Thyroid Center in Tampa, Florida, and Matthew Macer, M.D., the medical director at Halo Fertility in Los Angeles.

Hormones, particularly estrogen, might also increase women's likelihood of developing autoimmune and thyroid conditions, according to Vanessa Barboza, M.D., an endocrinologist and internist at Jersey City Medical Center in New Jersey.

Estrogen, which is far more abundant in women, peaks during puberty and is highest during the follicular stage of the menstrual cycle, from the start of your period until ovulation. Best known for its role in reproduction, estrogen also influences the immune system and thyroid in multiple ways.

Some researchers hypothesize estrogen levels in women could impact autoimmune gene expression on the X chromosome, elevating their risk of autoimmunity, Roy and Macer said.

According to Macer and Barboza, there's also some evidence that estrogen fluctuations associated with menstruation and pregnancy could contribute to the development of autoimmune and thyroid conditions.

"The regulation of hormones and reproductive health is far from black and white. In fact, there is so much 'cross talk' in our brain between nearly all the cells that make important hormones that it is quite common for a disturbance in one area to lead to a disturbance in another area," Macer said. "For instance, in women who have primary hypothyroidism, the body's response to increased thyroid production also leads to increased production of a hormone called prolactin—important for breastfeeding—which in turn can lead to irregular ovulation."

Estrogen prompts the thyroid to create thyroglobulin, a precursor to thyroid hormone. Without enough estrogen, the body won't produce enough thyroglobulin, and with too much estrogen—a condition known as estrogen dominance or unopposed estrogen—it will produce thyroglobulin in excess.

Estrogen also increases the production of thyroxine-binding globulin (TBG) in the liver. TBG, along with transthyretin and human serum albumin, is responsible for binding to thyroid hormones and transporting them throughout the body. Too much of this protein can suppress thyroid hormone availability, meaning the body can't properly use the thyroid hormones it produces.

Besides over- and underactive thyroid, estrogen dominance is associated with an increased risk of certain cancers, including thyroid cancer. Some research also indicates an association between polycystic ovary syndrome (PCOS), thyroid disorders and estrogen dominance.

"There is a clear correlation between PCOS and thyroid disorders, specifically, hypothyroidism," Roy said. "Hashimoto's is three times more common in patients with PCOS than those without PCOS. It may be due to the common factors predisposing women to both disorders, or there may be a pathophysiologic connection between them. It is likely multifactorial, but the definitive answer is not known yet.

"The woman's reproductive system is very complex, and thyroid hormones are vital for the proper functioning of the female reproductive system," Roy added.

Estrogen dominance can occur due to excess estrogen, insufficient progesterone or both. Typically, estrogen and progesterone cooperate and balance each other. But without enough progesterone to keep it in check, estrogen can tip the balance and cause a host of problems, even if its levels are within the typical range.

Other than insufficient progesterone, conditions that can contribute to estrogen dominance include:

• Being overweight
• Stress
• Liver problems
• Excessive alcohol intake
• Certain hormonal medications, such as high-dose oral contraceptives

Synthetic xenoestrogens—chemicals that mimic estrogen—can also increase estrogen levels. These include bisphenol A (BPA) and phthalates, commonly found in plastics, pesticides and household cleaning products.

Estrogen dominance symptoms mirror hypothyroidism and include:

• Fatigue
• Brain fog
• Weight gain
• Low libido
• Depression
• Intense PMS
• Irregular menstrual cycles
• Constipation
• Thinning hair
• Mood swings
• Headaches
• Bloating
• Water retention

Unopposed estrogen can increase a person's risk of conditions such as endometriosis, uterine fibroids and PCOS. It can also inhibit fertility.

"In response to the increased demands of the developing baby, there is an increase in thyroid production during pregnancy, especially the beginning, until the baby can start to produce its own thyroid hormone. This increase is actually from the pregnancy hormone known as hCG," Macer said.

Since hCG has a structure very similar to thyroid-stimulating hormone (TSH), it stimulates the thyroid to make more thyroid hormone during the first 10 weeks of pregnancy when hCG is rising.

"Once hCG starts to even out and then decrease later in pregnancy, the thyroid makes less hormone and falls back under the sole control of its normal growth signal, TSH," Macer said, adding that pregnancy usually offers some immunological protection against autoimmune disease.

However, because of the stress on the thyroid and hormonal fluctuations generally, some people develop autoimmune conditions a few months after giving birth.

"Some people will experience postpartum thyroiditis, when the thyroid becomes inflamed and overactive, within a year of having a baby," Barboza said. "We can identify via bloodwork if a person is at an increased risk of developing a thyroid condition during pregnancy so that they could be treated while pregnant."

Scientists aren't sure what causes postpartum thyroiditis, according to Johns Hopkins Medicine. But people with antithyroid antibodies before pregnancy and those with type 1 diabetes or a history of thyroid dysfunction are more likely to develop it.

Teitelbaum, Roy and Barboza noted a few additional reasons women may be more likely to receive a thyroid disorder diagnosis, including diet and their propensity to be more proactive about health screenings.

Diet

The thyroid needs iodine to produce thyroid hormone, so too little or too much can lead to hyper- or hypothyroidism. Iodine deficiency is relatively rare today in the United States, but it's still prevalent worldwide. According to Teitelbaum, the differences in how the bodies of men and women utilize iodine could contribute to the likelihood of developing a thyroid disorder.

"Iodine is critical for healthy thyroid and breast tissue. Low iodine has been associated with increased breast cancer risk. When a man's diet is low in iodine, it can all go to his thyroid," Teitelbaum said. "A woman must split the limited amount of iodine between her thyroid and her breast tissue. Food processing has been associated with a 50 percent loss of iodine intake over the last century."

Higher detection rates

Another reason women are more likely to be diagnosed with thyroid disorders is that they tend to be more proactive about their health, according to Roy.

"Historically, women take better care of themselves than men," she said. "Therefore, women are more likely to go see a physician and are more likely to have imaging tests performed. Many thyroid nodules are actually found incidentally on scans done for reasons other than the thyroid."

Once a nodule is detected, the healthcare provider should administer a complete thyroid evaluation, including an ultrasound and possibly a biopsy, Roy said. If the nodule appears suspicious, surgery may be recommended to mitigate cancer risk.

Thyroid disorders are fairly easy to detect and manage with help from a medical professional. If you don't have a regular doctor, telehealth makes finding one less stressful. Giddy telehealth makes it easy to get connected to a qualified healthcare professional who can help with a variety of conditions. You can connect with them through video visits, and many of them offer same-day appointments.